What is the purpose of the use of suction with a chest tube and drainage system?

Closed chest drainage systems use gravity and/or suction to restore negative pressure and remove air, fluid, and/or blood from the pleural space so that the collapsed lung can re-expand. Whenever a chest tube is inserted it must be connected to a one-way mechanism that allows air to escape from the pleural space while preventing air to enter from the atmosphere. This can be accomplished by using an underwater seal mechanism. Traditionally, chest drainage was accomplished with a three-bottle chest drainage system. The three-bottle system has been replaced by various disposable units that incorporate the traditional functions of the three-bottle system and integrates them into one plastic unit. Disposable chest drainage systems have a number of safety advantages over glass bottle systems as well as ease in set-up. Air or fluid can exit the pleural space as a result of gravity, but the water seal prevents it from being drawn back into the cavity.

The collection chamber is at the right side of the unit. The 6-foot tubing connects directly to the chest tube. Any fluid drainage from the chest goes into this chamber. It is usually calibrated in 1 ml increments up to 100 ml, 2 ml increments from 100 ml to 200 ml and 5 ml increments from 200 ml to 2500 ml. It has a surface that can be marked with the time and date of drainage.

The water seal chamber is the middle chamber. When this chamber is filled with fluid up to the 2 cm line, a 2 cm water seal is established. A short latex tube at the top of this chamber is either left open to air for gravity drainage or attached to a suction source. The water seal chamber should have fluid gently bubbling immediately upon insertion of the chest tube, during expiration and with coughing. In addition to maintaining the original purpose of the water seal – keeping air from entering the pleural cavity the system has a calibrated manometer in the water seal chamber to measure the amount of negative pressure referred from the pleural cavity. The water level in the water seal manometer rises as intrapleural pressure becomes more negative. The water level in the water seal should be monitored routinely to check for evaporation. Continuous bubbling in this chamber indicates a leak in the system. Fluctuations in the water level in the water-seal chamber of 5 to 10 cm, rising (during inhalation) and falling (during expiration), should be observed with spontaneous respirations. If the patient is on mechanical ventilation, the pattern of fluctuation will be just the opposite. Additionally, if suction is being applied, this must be temporarily disconnected to correctly assess for fluctuations in the water-seal chamber.

The systems have high negativity float valves in the top of the water seal chamber. This maintains the water seal in the event of high negative intrapleural pressures, as may occur with the deep breath taken before vigorous coughing, or with forced inspiration from an upper airway obstruction. High negativity can also occur if the chest tubing is stripped. High negativity is indicated by rising water in the water seal chamber. Depressing the high negativity relief valve will allow filtered air into the system, relieving negativity and allowing the water level to return to baseline in the water seal. In instances of falsely imposed high negative pressure, such as stripping chest tubes, water will continue to rise, filling the high negativity relief chamber at the top of the water seal chamber. This relief chamber will automatically vent excessive negative pressure, which will prevent respiratory compromise from accumulated negativity. Water spillover into the collection chamber is also minimized.

The systems also have positive pressure relief valves. They remain closed when suction is applied to the system, but open whenever pressure within the system becomes positive. Since the only way for air to leave the system is through the suction port, obstruction of the suction line (by rolling the bed on top of the tubing, for instance) could cause accumulation of air in the system leading to tension pneumothorax. This safety feature not present in the glass-bottle system, allows venting of the positive pressure, minimizing the risk of a tension pneumothorax.

The patient air leak meter is made up of a number of numbered columns, reading from 1 (low) to 7 (high). As air flow through the system increases, bubbling will occur toward the higher end of the scale. Decreasing flow will result in bubbling on the lower end of the scale. This feature provides an indication of air leak magnitude, allowing the clinician to monitor air leak increase or decrease as therapeutic interventions (such as adding or increasing PEEP) are made.

The suction control chamber is the chamber on the left side of the unit. The units come with two mechanisms to regulate the amount of suction transmitted to the pleural space: wet or dry suction.  Wet suction regulates the amount of suction by the height of a column of water in the suction control chamber.  Note, it is the height of a column of water, not the setting of the suction source that actually limits the amount of suction transmitted to the pleural cavity.  A suction pressure of –20 cm H2O is commonly recommended, but lower levels may be required for infants and for patients with friable lung tissue, or if ordered by the physician.

To use wet suction, the suction control chamber is filled with sterile water to the desired height.  Connect the tubing supplied with the unit to suction tubing, and then to the suction source.  Adjust the source suction to produce gentle bubbling in the suction control chamber.  The appearance of gentle bubbling assures you that the amount of suction set (by the height of the column of water) is the amount of suction being applied to the chest cavity; excess suction is vented through the bubbling. Increasing suction at the suction source will increase airflow through the system; it will have minimal effect on the level of suction imposed on the chest cavity.

Excessive source suction will not only cause loud bubbling (which can disturb patients and caregivers), but will also hasten evaporation of water from suction control chamber; decreasing the suction applied to the chest cavity. Self-sealing diaphragms are provided to adjust the water level in this chamber should overfilling or evaporation occurs.

The dry suction control chamber is even easier to use. Instead of regulating the level of suction with a column of water, suction is controlled by a self-compensating regulator. A dial on the side of the suction control chamber allows for the desired level of suction to be set according to the physician’s order. As with the wet unit, the short tubing supplied with the unit is connected to the suction source. The source must provide a minimum of 20 LPM of airflow. Once connected to suction, increase the level of suction until the float appears in the suction indicator window. The visual confirmation of suction pressure provides the same assurance as the gentle bubbling (patient air leak) or changes in suction pressure (surge/decrease at the suction source). With the dry suction unit, the level of suction set can be increased at any time.

Not all patients require suction. Suction may be discontinued to transport a patient; it may be discontinued 24 hours before chest tube removal. If suction is discontinued, make sure the suction tubing remains open to atmosphere to allow air to leave the drainage system unless suction is discontinued at the same time as the clamping of the chest tube.

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